Disease Control and Pest Management

The Influence of Several Crop Sequences on the Incidence of Verticillium Wiltof Cotton and on the Population of Verticillium dahliae in Field Soil

E. J. Butterfield, J. E. DeVay, and R. H. Garber

Department of Plant Pathology, University of California, Davis, CA 95616, and USDA-ARS, U.S. CottonResearch Station, Shafter, CA 93263. Present address of senior author: Boyce Thompson Institute for Plant Research,Inc., Yonkers, NY 10701.

Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by theU.S. Department of Agriculture and does not imply its approval to the exclusion of other products that may also besuitable.

The authors thank the California Planting Cotton Seed Distributors, Bakersfield, for their financial support of thisresearch and J. S. Pullman for technical assistance.

Accepted for publication 27 February 1978.

ABSTRACT

BUTTERFIELD, E. J., J. E. DE VAY, and R. H. GARBER. 1978. The influence of several crop sequences on the incidence ofVerticillium wilt of cotton and on the populations of Verticillium dahliae in field soil. Phytopathology 68: 1217-1220.

Since Verticillium dahliae was not detectable by soil assay and/or rotations with grain sorghum or dry fallow did notor by subsequent infection of cotton plants, it was considered change the concentration of V. dahliae propagules in soil.to be eradicated from most field test plots following a I-yr Significant (P = 0.05) decreases in disease incidence androtation between cotton and paddy rice (continuous increases in cotton lint yields resulted from rotations withflooding). In contrast, populations of V. dahliae per gram of paddy rice, perennial ryegrass, and- in some fields fromsoil were increased with rotations to safflower or with safflower, grain sorghum, or frequent soil irrigation followedcontinuous cotton. Keeping soil wet but not flooded for 6 wk by grain sorghum.

Verticillium wilt of cotton, incited by Verticillium technique (1) was used in the present study.dahliae Kleb., is the major disease problem in the Numbers of soilborne propagules of V. dahliae in soilproduction of cotton in the USA. In California, the have been reduced by periods of flooding. Menzies (8)disease is now partially managed by the use of wilt- found that 6 wk of open field flooding reduced thetolerant Acala cultivars (Gossypium hirsutum L.) but concentration of V. dahliae to undetectablestrains of V. dahliae highly virulent to those cultivars are concentrations, as indicated by soil assay or by baitingprevalent (12) and cause significant losses in yield. with susceptible tomato plants. Disappearance ofTarping and deep placement of fumigants have reduced propagules was hastened by amendment of soil with 1%the incidence of Verticillium wilt in cotton (3,15) but have alfalfa meal or 0.1% sucrose. Using artificially infestednot eradicated the fungus from field soils. Erratic plant soil in laboratory studies, Nadakavukaren (10) obtainedresponses and high costs, however, have presently similar results. All infectivity and all detectableeliminated soil fumigation for control of Verticillium wilt propagules were eliminated within 2 mo in soils held atin cotton. Systemic fungicides and growth-regulating field capacity at temperatures of 10 C or higher. At 30 Ccompounds have shown promise for control of all propagules were eliminated within 14 days. InVerticillium wilt but their use is not economically feasible California, cotton growers in Fresno County whoat present (4). Improvements in cotton yields and practice rotation with rice have observed that thisreduction of disease severity have been reported in rotation is effective in reducing Verticillium wilt innumerous studies (11) involving the interruption of following cotton crops.continuous cotton culture with other crops or with The objectives of this study were to compare the effectsfallowing. The use of cultural practices, including crop of continuous flooding vs. frequent soil irrigation, androtations, for management of Verticillium wilt has been paddy rice vs. other rotation crops on the survival of V.reviewed by Ranney (11). Attrition of propagules of V. dahliae, on the incidence of Verticillium wilt in cotton,dahliae under nonhost crops is slow (6) and evidence and on cotton lint yields.indicates that even long rotations of planting tononsusceptible crups do not eliminate V. dahliae from the MATERIALS AND METHODSsoil (13). The development of a dry soil assay techniqueusing an Anderson Sampler (2, 5) has provided a reliable Crop rotation studies.-Field experiments consisted ofmethod to estimate the numbers of propagules of V. 2-yr crop rotations at Five Points, Shafter, and Davis,dahliae in field soil. A further modification of that California. Two separate experiments were conducted at

the Five Points location where the area used for the00032-949X/78/000 217$03.00/0 experiments had been cropped to cotton and foliarCopyright © 1978 The American Phytopathological Society, 3340 symptoms of Verticillium wilt had appeared in 15 to 30%Pilot Knob Road, St. Paul, MN 55121. All rights reserved, of the plants. Soil assays for V. dahliae indicated an

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1218 PHYTOPATHOLOGY [Vol. 68

average population of about 20 propagules per gram of at 120 propagules per gram of soil. In 1971, alternate 8.1-soil with no field areas of significant variation observed, m-wide strips of the plot were planted to perennialThe experimental plot consisted of six replications of five ryegrass (Lolium perenne L.) sod. The sod wastreatments. Each individual treatment plot was maintained during 1972 when other rotations wereapproximately 8 X 40 m and was separated from planted in the nonsoded areas. The rotation treatmentsadjoining plots by a 1.5-m levee which remained in place were the same as those described for the Shafter testthroughout the experiment. The first treatment was a dry except deletion of the dry fallow. Each treatment wasfallow maintained weed free by hand-hoeing with no replicated four times and the plot sizes were 8 X 8 m. Inadditional cultivation or irrigation. The second treatment 1973, the sod was plowed under and the entire plot was(wet-sorghum) consisted of a three-times-weekly planted to Acala SJ-1 cotton.application of 4-6 cm of water from 20 April through 7 Soil assays for Verticillium dahliae.-The inoculumJune (105 cm total). Surface water remained no more densities of V. dahliae in the test plots were analyzed withthan 12 hr after the end of each application. Grain an Anderson Sampler using the technique of Butterfieldsorghum [Sorghum bicolor (L.) Moench 'NK 125'] then and DeVay (1). The standard error by this method was 10-was planted on 15 June in double rows on raised beds, 102 12%. A subplot of approximately 60 m 2 was establishedcm from center to center. The third treatment (dry- within each treatment replicate. These subplots weresorghum) consisted of grain sorghum planted 15 June sampled at least four times during each year of the test byafter the plot had received the normal single preirrigation taking twelve 30 X 2.5-cm cores from each. The coresof 15 cm. In both sorghum treatments the grain was from each subplot were bulked, air dried, subsampledremoved at maturity and the plant debris was three to five times, and analyzed to determine the numberincorporated into the soil. The fourth treatment was of V. dahliae propagules per gram of air-dried (6-wk) soil.planted with Verticillium wilt-susceptible safflower Rating of root vigor and disease.--Following the(Carthamus tinctorius L.). The fifth treatment was cotton harvest at Shafter, the plots were irrigated and 30planted to cotton cultivar Acala SJ-1. cotton plants from each plot were removed at random.

A following study at the same location utilized 15 wk of Each root system was visually rated for vigor and thesoil flooding with rice (Oryza sativa L. 'Colusa 1600'). The presence of root disease lesions.water level within the plots was maintained at a depth of Isolation of Thielaviopsis basicola from field15-30 cm by the continuous addition of fresh water. No soil.-Soil samples from the test plot at Shafter wereoutlet was provided for surface water circulation. Other baited with fresh carrot disks to determine the presence oftreatments in this same test included dry fallow, cotton, T. basicola (Berk. & Br.) Ferr. For each subplot, 10 freshand two cultivars of safflower. One safflower cultivar was carrot disks were treated with 5 g of soil, moistened withGila which is susceptible to Verticillium wilt and the other 50 Mg/ ml streptomycin sulfate in water, and incubated forwas an experimental cultivar which is resistant to 3 days. Then the soil was washed away and the disks wereVerticillium wilt. All plots were planted to Acala SJ-2 incubated for an addition 7 days after which each disk wascotton in the second year of the tests. Plot sizes were scored for the presence or absence of T. basicolasimilar to those of the previous study and were similarlyseparated by permanent levees. Yield data in all cottonplots were obtained by machine harvesting the center six RESULTSof eight 40 m rows and weighing the seed cottonimmediately. No significant variations in moisture Soil flooding, as practiced with rice culture in the 1974content were found. trial at Five Points, was the most effective treatment for

Field experiments at Shafter were conducted in an area reducing the population of V. dahliae in soil (Table 1).in which the preceding cotton crop had a moderate The average reduction in inoculum density wasincidence of foliar symptoms of Verticillium wilt (30- approximately 95% in 1 yr. The fungus was not detectable60%). Soil assays indicated an average inoculum density by soil assay and it did not cause infection of theof about five propagules per gram of soil. One field area subsequent cotton crop in four of the six replications. Thewith a much greater inoculum density was detected and only other treatment that reduced the initial populationdata from it were not used in the tabulation of results. of V. dahliae was the rotation to perennial ryegrass sod

Eight replications of four treatments were placed in a which caused an 80% reduction in inoculum density.randomized block design. Each plot was 8 X 20 m and was In contrast to the continuous flooding treatment withseparated from adjoining plots by a 1.5-m-wide levee. The paddy rice, frequent soil irrigation for 6 wk at Shafter,first treatment was dry-fallow as previously described. Five Points (1972), and at Davis (wet-sorghum) resultedThe second treatment (wet-sorghum) received a weekly in no significant decreases in inoculum densities.application of 15 cm of water from 20 April through 7 Similarly, 1-yr rotations to either dry fallow or grainJune (105 cm total). Grain sorghum was planted on 15 sorghum caused little or no change from the inoculumJune. The third and fourth treatments were grain densities of V. dahliae found in 1972. Inoculum densitiessorghum (dry-sorghum) and cotton as previously increased under continuous cotton at Shafter and Fivedescribed. All plots were planted to Acala SJ-1 cotton in Points and rotation to safflower (another host crop)the 2nd yr of the study. caused increases in inoculum densities in both tests at

The third location at Davis is 160 km north of most Five Points. Inoculum density of the continuous cottoncommercial cotton fields in California. In the year before treatments at Davis did not increase during the period ofthese experiments, 80 to 100% of the cotton plants grown the test.at this location had foliar symptoms of Verticillium wilt. A strong association existed between inoculum densityThe average inoculum density of V. dahliae was measured and foliar and vascular wilt symptoms at Shafter. An

August 1978] BUTTERFIELD ET AL.: VERTICILLIUM/CROP SEQUENCE 1219

association also existed between reduced cotton lint soilborne propagules of V. dahliae, reduction ofyields and higher inoculum densities as well as higher Verticillium wilt incidence, and increasing cotton lintincidences of foliar and vascular wilt symptoms at yields. In view of the work of Menzies (8) andShafter. At Five Points in 1973, the percentage of cotton Nadakavukaren (10), the importance of the rice plants forplants with foliar symptoms of wilt was reduced following the eradication of V. dahliae is unknown but income fromfallow, wet-sorghum, or safflower compared to that crop does make it more economically attractive. Wecontinuous cotton or sorghum. Similarly at Davis, cotton observed no decline in numbers of propagules in plotsfollowing ryegrass was more vigorous and had fewer that received frequent irrigation. This would sustain theplants with foliar and vascular wilt symptoms than did conclusions that soil saturation is required for rapidcotton following other treatments. elimination of propagules of V. dahliae (8, 10). Moore (9)

Root systems of cotton plants grown at Shafter and Stoner and Moore (14) made similar observations infollowing dry fallow, wet-sorghum, or sorghum were their studies of Sclerotinia sclerotiorum in Florida. Theystrikingly more vigorous and free from root discoloration observed that decomposition of sclerotia occurred muchthan were the roots of plants from the continuous cotton more rapidly under flooded and rice paddy conditionsplots (Table 2). Isolations from the root lesions were not than under conditions of frequent water application.attempted but T. basicola was isolated readily from the Apparently the decreases in inoculum density andsoil samples taken from the test plots by using the carrot disease incidence are directly related to the effects ofdisk assay. There was a strong relationship between the flooding on the propagules of V. dahliae. The observednumber of disks colonized and the amount of root increases in lint yield are due also (at least in part) to thediscoloration observed (Table 2). reduced incidence of Verticillium wilt. Other less well

recognized soil pathogens also may be affected by theDISCUSSION flooding and thus affect yields. Kelman and Cook (7)

indicated that the low incidence of soilborne plantContinuous soil flooding associated with culture of diseases in certain parts of the People's Republic of China

lowland rice was highly effective for the eradication of may be due to the extensive culture of paddy rice. The

TABLE 1. Effect of various cultural practices on the population of propagules of Verticillium dahliae in soil, the incidence ofVerticillium wilt, and lint yields of Acala SJ-1 cotton at two California locations

Initial Plants with:Location Rotation treatment prop./g Prop. / g

soil soil Foliar Vascular Yield of1972 1973 (May 72)a (May 73) symptomsb symptomsc lint/ hectare'

(no.) (no.) (%) (%) (kg)

Shafter Fallow Cotton 2 x l x 0.8 x 14.6 x 1,185 xWet-sorghum Cotton 3 x 4 x 1.8 x 36.7 x 1,320 xDry-sorghum Cotton 5 x 4 x 0.8 x 24.6 x 1,181 xCotton Cotton 5 x 18 y 7.8 y 78.8 y 998 v

Five Points Fallow Cotton 23 x 15 x 36.0 x n.c.d 1,283 xWet-sorghum Cotton 23 x 18 x 43.7 x n.c. 1,068 yDry-sorghum Cotton 12 x 20 x 52.1 y n.c. 1,218 xCotton Cotton 21 x 38 y 59.8 y n.c. 1.112 ySafflower

(susceptible) Cotton 28 x 40 y 40.6 x n.c. 1.299 x(cm)

Davis Dry-sorghum Cotton 140 x 131 x 85.0 x 99.7 x 88.5 xWet-sorghum Cotton 128 x 124 x 85.1 x 98.0 x 97.7 xCotton Cotton 122 x 129 x 96.2 x 99.3 x 91.6 xRyegrass Cotton 60 y 24 y 47.7 y 76.7 y 112.9 v

1974 1975 (May 74) (May 75) (kg)Five Points Fallow Cotton 63 x 61 x 80.8 x 97.5 x 1,058 x

Paddy rice Cotton 51 x 3 y 2.3 y 3.3 y 1,711 vSafflower

(resistant) Cotton 40 x 52 x 77.5 x 95.7 x 1,086 xCotton Cotton 45 x 57 x 95.5 x 100.0 x 1,004 xSafflower

(susceptible) Cotton 42 x 66 x 73.4 x 93.8 x 1,148 x

'Numbers followed by different letters differ significantly (P = 0.05) within each test plot location.

hThe percentage of plants with foliar symptoms of Verticillium wilt immediately before defoliation for harvest, second year ofstudy.

cThe percentage of plants with vascular discoloration of the main stem immediately following harvest, second year of study.dThe abbreviation n.c. = not counted.'At the Davis location, lint yields were unavailable. Figures represent plant height (cm).

1220 PHYTOPATHOLOGY [Vol. 68

TABLE 2. Effect of various cultural practices on root vigor Phytopathology 67:1073-1078.and disease development in cotton roots and the relative soil 2. DE VAY, J. E., L. L. FORRESTER, R. H. GARBER, andpopulations of Thielaviopsis basicola E. J. BUTTERFIELD. 1974. Characteristics and

concentrations of propagules of Verticillium dahliae inRoot Colonization of air-dried soils in relation to the incidence of Verticillium

Treatment Diseased Diseased vigor carrot disks wilt of cotton. Phytopathology 64:22-29.roots' roots ratingb by T. basicolac 3. DE VAY, J. E., 0. D. MC CUTCHEON, A. V.(no.) (%) (%) RAVENSCROFT, H. W. LEMBRIGHT, R. H.

Fallow 0.9 x 2.9 2.3 1 X GARBER, D. E. JOHNSON, M. HOOVER, and J.Wet-sorghum 3.3 x 10.8 2.4 7 x QUICK. 1970. Fumigation and other chemicalDry-sorghum 3.1 x 10.4 2.3 6 x treatments for control of Verticillium wilt and potashCotton 12.4 y 41.3 1.8 30 y deficiency symptoms in cotton. Pages 218 - 226 in

Cotton disease research in the San Joaquin Valley,"Average number of diseased roots out of 30 roots per California. Research reports for 1968-1969. Div. of Agric.

replication for eight replications. Numbers followed by the same Sci., Univ. of California, Berkeley. 251 p.letter are not significantly different (P = 0.05). 4. ERWIN, D. C., R. H. GARBER, L. CARTER, and T. E.

"Average rating of 30 root systems per replication for eight DE WOLF. 1969. Studies on thiabendazole and benlatereplications. Scale: 0 = tap root blackened with few or no lateral as systemic fungicides against Verticillium wilt of cottonroots; 3 = vigorous and apparently healthy root. in the field. Page 29 in Beltwide Cotton Production

cPercent of carrot disks colonized from soil overlays. Ten disks Research Conferences. 29th Cotton Disease Council.per 5 g soil per replication, eight replications. National Cotton Council, Memphis, Tennessee. 134 p.

5. HARRISON, H. D., and C. H. LIVINGSTON. 1966. Amethod for isolating Verticillium from field soil. Plant.

chemical and physical changes in the soil caused by Dis. Rep. 50:897-899.prolonged flooding also may be involved in the yield 6. HUISMAN, 0. C., and L. J. ASHWORTH, JR. 1976.increase. Influence of crop rotation on survival of Verticillium

Of the other rotations studied, only perennial ryegrass albo-atrum in soils. Phytopathology 66:978-981.was effective in reducing the inoculum density of V. 7. KELMAN, A., and R. J. COOK. 1977. Plant Pathology indahliae. Sewell and Wilson (13) observed that the People's Republic of China. Annu. Rev. Phytopathol.populations of V. albo-atrum were greatly reduced in soil 17:409-429.

under a ryegrass sod but disease potential from V. dahliae 8. MENZIES, J. D. 1962. Effect of anaerobic fermentation inwas still present after 4 yr of sod. They were not able to soil on survival of sclerotia of Verticillium dahliae.

monitor the population of V. dahliae, however, so the Phytopathology 52:743 (Abstr.).effect of the sod on the total population is unknown. it 9. MOORE, W. D. 1949. Flooding as a means of destroying the

sclerotia of Sclerotinia sclerotiorum. Phytopathologydoes indicate that this treatment may not eradicate V. 39:920-927.dahliae. 10. NADAKAVUKAREN, M. J. 1960. The effect of soil

The other rotations examined in this study did not moisture and temperature on the survival of Verticilliumresult in reduction in numbers of V. dahliae propagules microsclerotia. Ph.D. Thesis. Oregon State University,and the responses of the following cotton crop were Corvallis. 64 p.variable. Huisman and Ashworth (6) also observed the II. RANNEY, C. D. 1973. Cultural control. Pages 98 - 104 inlack of rapid attrition of propagules in the presence of Verticillium wilt of cotton. Proceedings of a worknonhost crops such as wheat and corn. Our results also conference. National Cotton Pathology Researchindicate that the potential of crop rotation for effective Laboratory, College Station, Texas. 134 p.management of Verticillium wilt is limited in fields with 12. SCHNATHORST, W. C., and D. E. MATHRE. 1960. Hostrange and differentiation of a severe form of Verticilliumhigh infestations of V. dahliae. In areas where the culture gange-and i n tiaton o pa th ol o f 50:1155-1161

of lwlad rie o peennil regrss i fesibe, rtatons albo-atrum in cotton. Phytopathology 50:1155-1161.of lowland rice or perennial ryegrass is feasible, rotations 13. SEWELL, G. F. W., and J. F. WILSON. 1966. Verticilliumwith these crops could be important in the management of wilt of the hop: the survival of V. albo-atrum in the soil.Verticillium wilt of cotton and other susceptible crops. Ann. Appl. Biol. 58:241.

The information presented here on the effect of 14. STONER, W. N., and W. D. MOORE. 1953. Lowland ricerotations on cotton root rot incidence and T. basicola farming, a possible cultural control for Sclerotiniapopulations is not extensive enough to support sound sclerotiorum in the Everglades. Plant. Dis. Rep. 37:181-conclusions. Nevertheless, it does illustrate that the plant 186.responses observed in this test may not be attributable 15. WILHELM, S., A. G. GEORGE, W. PENDRY, and J. E.solely to suppression of Verticillium wilt. SAGEN. 1966. Soil fumigation to control Verticillium

wilt of cotton and the nature of the fumigation inducedLITERATURE CITED stunting. Pages 65 - 68 in Cotton disease research in the

San Joaquin Valley, California. Research reports forI. BUTTERFIELD, E. J., and J. E. DE VAY. 1977. 1965. Div. of Agric. Sci., Univ. of California, Berkeley. 82

Reassessment of soil assays for Verticillium dahliae. p.